/Engine/Source/Editor/VREditor/Public/VREditorMode.h
General way to spawn an external SlateUI from a radial menu
void UpdateExternalSlateUI ( [TSharedRef](API\Runtime\Core\Templates\TSharedRef)< [SWidget](API\Runtime\SlateCore\Widgets\SWidget) > InWidget, [FName](API\Runtime\Core\UObject\FName) Name, FVector2D InSize )